I always use this example to counter that argument:
What if you're a ruby player and you get injuries from playing the sport over a long time. You end up having a bad knee injury and find it difficult to walk. Is that not a disability? The rugby player could have chosen to not play at any point so it's completely within their control to prevent it.
Or if you have an injury that makes you disabled. But you don't do the months or years have hard physio that is needed. Do we say nope your fault. No different to not doing the hard work of losing weight.
what a great idea - give it time and you'll get the young kids down at the local car park/disablility ramp with them all pimped out 